1. Field of the Invention
This invention relates to a solar cell module and a process for its production, and more particularly to a solar cell module having a high reliability, which can have a great variety of shapes given by working its regions embracing photovoltaic devices. This invention also relates to a solar cell module installing method and a solar electricity generation system which make use of the solar cell module.
2. Related Background Art
In recent years, an increase in conceousness about energy source protection and environmental problems is spreading worldwide. In particular, people have a serious anxiety about the exhaustion of oil and the phenomenon that CO2 emissions make the earth""s environment warm. Accordingly, solar cell energy, produced by converting solar energy directly to electric power and being a clean energy, are considered greatly hopeful.
Solar cells presently in use have various types including those making use of crystalline silicon and those making use of amorphous silicon.
In particular, amorphous silicon solar cells comprising a conductive metal substrate and a transparent conductive layer formed thereon are more inexpensive and light-weight than solar cells making use of crystalline silicon solar cells and also are rich in impact resistance and flexibility, thus they are considered promising. Recently, they are installed on roofs, walls and so forth of buildings, making the most of the advantages that they are light-weight, have a superior impact resistance and are flexible, which are characteristic features of the amorphous silicon solar cells. In such an instance, reinforcing materials are laminated to solar cells on their non-light-receiving sides via adhesives or the like so that they can also be used as construction materials. Laminating reinforcing materials in this way can make solar cell modules have a higher mechanical strength and can prevent them from warping or deforming because of temperature changes. Especially, since more sunlight can be taken in, it is done positively to install such solar cell modules on roofs. When used on roofs, in conventional steps, frames are attached to solar cells, a stand is set on a roof and the solar cells are further set on the stand. In contrast to such procedure, solar cell modules provided laminately with reinforcing materials can be set directly as roofing materials, the reinforcing materials being worked by bending. Thus, since material cost can be cut down greatly and the number of operation steps can also be lessened greatly, it becomes possible to provide inexpensive solar cell modules. Also, since it is unnecessary to provide frames and stands, a very light-weight solar cell set can be set up. More specifically, such a solar cell set can be dealt as a metal roof which attracts notice recently because of its superior installation operability, light weight and superior earthquake resistance.
For example, a roofing material integral type solar cell module disclosed in Japanese Patent Application Laid-Open No. 7-302924 is worked in the same way as roofing materials usually available, and hence can be installed in a good operability. When it is worked, molding machines used conventionally can be used as they are, can be handled with ease and are available at a low cost. However, in this solar cell module, photovoltaic devices are positioned at a flat area of a flat panel lateral roofing material, and the photovoltaic devices are not deformed at all in structure.
In order for the roofing material integral type solar cell module to be light-weight and so formed as to be able to be worked in the same way as usual roofing materials, the module may preferably be formed in such a way that amorphous silicon semiconductors are sealed insulatingly with a resin on a steel sheet used conventionally as a roofing material.
FIGS. 1A and 1B are a plan view and a cross-sectional view, respectively, which illustrate diagrammatically an example of a solar cell module. In FIGS. 1A and 1B, reference numeral 1101 denotes a surface protective material; 1102, a filler; 1103, a photovoltaic device; 1104, a back protective material; and 1105, a reinforcing material.
Recently, there is a tendency of attaching importance to individual originality, and construction materials and solar cells are no exception to such tendency. In order to continue to prepare solar cells and construction materials having a great variety of shapes adapted to various needs, what is necessary is not to always keep the region of a photovoltaic device flat but to ensure workability at all regions embracing the photovoltaic device.
As an example adaptable to such a variety, Japanese Patent Application Laid-Open Nos. 8-222752 and 8-222753 and Japanese Patent Publication No. 6-5769 disclose corrugated solar cell modules. In all publications, an example is shown in which photovoltaic devices are arranged in the form of waves so that light can be utilized in an improved efficiency. The photovoltaic devices are, e.g., bonded with an adhesive to a steel sheet worked into a corrugated sheet.
In the above example, however, the stress that applies to photovoltaic devices is not taken into account when the photovoltaic devices are worked into waves. More specifically, all the amount of deformation in a substrate, the amount of deformation in a photovoltaic device and the amount of deformation as a solar cell module are not taken into account. The publications also do not refer at all to any influence of stress or deformation applied and any reliability against these.
Incidentally, the relationship between an a-Si:H (hydrogenerated amorphous silicon) layer and its strain is reported in, App. Phys. Lett. 54(17), 1989, pp.1678-1680, xe2x80x9cElectrical Properties of Hydrogenerated Amorphous Silicon Layers on Polymer Film Substrate under Tensile Stressxe2x80x9d. In this publication, reported is a change in resistance in a dark state when an a-Si:H layer (0.5 xcexcm thick, composed chiefly of i-type a-Si:H) is formed superposingly on a PET (polyethylene terephthalate) substrate (100 xcexcm thick) and the a-Si:H layer is tensed. Details of this report are as follows: When the a-Si:H layer is tensed, the resistance becomes gradually higher (reversible) until 7,000 xcexcxcex5 (elongation of 0.7%) because of the piezoelectric effect, and the resistance increases abruptly (irreversible) above 7,000 xcexcxcex5 because weak Sixe2x80x94Si bonds are cut off. It, however, is reported that the a-Si:H layer having increased in resistance as a result of the straining to above 7,000 xcexcxcex5 returns to the original state upon annealing at 150xc2x0 C. for 1 hour.
Nevertheless, this report neither discloses nor suggests that photovoltaic devices having been strained are put into use or that photovoltaic devices are made into a module in the state the devices have been strained. In addition, it concerns no evaluation at all on the reliability of the solar cell module whose photovoltaic devices have been strained.
J. App. Phys. 66(1), 1989, pp.308-311, xe2x80x9cEffect of Mechanical Strain on Electrical Characteristics of Hydrogenated Amorphous Silicon Junctionsxe2x80x9d also reports a piezoelectric effect of a-Si:H having p-i-n junction. Details of this report are as follows: When a-Si:H having p-i-n junction is strained in parallel to the p-i-n junction, electric currents decrease by 8% in both the forward direction and the backward direction (a dark state). Also, electric currents increase by 8% under application of a compression stress of 7,500 xcexcxcex5.
Since, however, at any event the reliability in use of photovoltaic devices having been strained is unclear, it has been avoided to work photovoltaic devices by applying stress or deformation thereto to prepare solar cell modules. Even if worked into a shape, their reliability in such shape must always be examined continually. In usual instances, many reliability tests must be made on one product (on its shape and strain after working), and hence it takes a very long time to bring one product into a finished product. More specifically, such a manner can not be expected to enable manufacture at the speed adaptable to the present demand for solar cells and construction materials which are sought to be available as a great variety of products.
The present invention has been made taking account of the above problems. An object of the present invention is to provide a solar cell module and a solar electricity generation system which have a high reliability over a long period of time.
Another object of the present invention is to provide a solar cell module that can give a superior beauty and design.
In addition, an object of the present invention is to provide a sollar cell module with an excellent workability.
Still another object of the present invention is to provide a solar cell module that can be installed with ease and can enjoy a low cost.
A further object of the present invention is to provide a solar cell module installing method and a solar electricity generation system that are rich in reliability, can be installed well and can enjoy a low cost, which make use of such a solar cell module.
A still further object of the present invention is to provide a process for producing a solar cell module which can achieve the above objects.
To achieve the above objects, the present invention provides a solar cell module comprising a photovoltaic device having a flexible substrate, wherein the photovoltaic device has a strain at least partly in the planar direction of the flexible substrate, and the strain is set not more than a critical value at which the photovoltaic device cracks; and provides a method of installing such a solar cell module by the use of a fixing member, and a solar electricity generation system having the solar cell module.
The present invention also provides a process for producing a solar cell module comprising a photovoltaic device having a flexible substrate, which process comprises a working step of causing the photovoltaic device to have a strain at least partly in the planar direction of the flexible substrate; the strain being set not more than a critical value at which the photovoltaic device cracks.